Sooo... I just spent $10 on this app and the keys from C0 through C1 just do not work. They make no sound. Only keys from C2 and up make any noise.

I am on a LG K8+ smart phone operating on Android. I already switched on Multi Core Processing, and it didn't change anything. There's still no sound. I see no other settings. Am I about to need a refund, or is there a fix? Thanks.